Deflecting system for cathode ray devices



June 17, 1941. R. B. DOME 2,246,168

DEFLECTING SYSTEM FOR CATHODE RAY DEVICES Filed June 29, 1939 Inventor: Robert B. Dome,

b9 AW His Attorneg.

Patented June 17, 1941 DEFLECTING SYSTEM FOR CATHODE RAY DEVICES Robert B. Dome, Bridgeport, Conn, assignor to General Electric Company, a corporation of New York Application June 29, 1939, Serial No. 281,898

Claims.

My invention relates to an improved system for controlling the deflection of the cathode rays in a cathode ray tube. More particularly, it relates to an improved system for supplying to each of a pair of deflecting electrodes in a cathode ray tube potentials which vary in symmetrical manner above and below an average or mean potential for controlling, in the desired manner, the deflection of the cathode ray beam.

Cathode ray tubes of the deflecting electrode type are provided with pairs of deflecting electrodes. The deflecting electrodes are normally connected to a control system which periodically supplies between the electrodes deflection controlling potentials, commonly of saw-tooth wave shape. In addition to the deflection controlling potential, the deflecting electrodes normally are maintained at an elevated and relatively constant potential above the potential of a cathode provided in the cathode ray tube. The potentials thus supplied to the deflecting electrodes effect a periodic variation of the course followed by the cathode ray electron stream and cause the electron stream periodically to sweep across the fluorescent screen provided in the end of the cathode ray tube.

Since the sweeping action of the cathode ray electron stream across the fluorescent screen must occur in accordance with a predetermined plan determined by the Wave shape of the deflecting potentials, any factors which produce a deviation in the movement of the cathode ray different from the predetermined plan operate to cause a certain amount of distortion of the recurrent image pattern formed on the tube fluorescent screen. A source of such distortion has heretofore been caused by undesirable pulsations occurring in the otherwise constant value of unidirectional potential which is used to maintain each of the deflecting electrodes at an elevated potential relative to the cathode of the tube. It has for this reason been necessary prior to applicants invention to use well designed and relatively expensive filters for the purpose of eliminating any slight fluctuations which might otherwise occur in the value of the unidirectional potential supplied to the deflecting electrodes. Filters of this nature are especially costly in that they must be insulated to withstand relatively high values of potential in the order of several thousand volts.

An object of my invention is to provide a defleeting control system for a cathode ray tube which dispenses with the necessity of the aforementioned filter.

A further object of my invention is to provide a deflecting control system having amplifying and inverting stages and one wherein pulsations occurring in a source of electrode potential for the cathode ray tube have no detrimental effect on the operation of the cathode ray device.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and means of operation, together with further objects and advantages thereof, may best be understood by referring to the following description taken in connection with the single figure of the accompanying drawing which illustrates an embodiment or" my invention.

Referring to the drawing, periodic deflecting potentials having a predetermined wave form are supplied from a source, not shown, through an input circuit lEi, H and a coupling condenser i2 to a control grid l3 of an electron discharge amplifier i i. A suitable operating bias for the control electrode it is provided by a cathode resistor i5 and parallel connected condenser I6 which are positioned between the cathode ll of the device ii and ground, this biasing potential being supplied to the control electrode through a resistor it. The device it is provided with an anode element l9 to which operating potential is supplied from a source iii through a resistor 2 l The deflecting potentials supplied through the input circuit it, l l are amplified by the discharge device 14 and appear in amplified form across the resistor iii. A portion of the output is supplied through a conductor 22 and a coupling condenser 23 to a control electrode 2d of a second electron discharge device 25. The device 25 has a cathode 28 which is connected to ground through the resistor iii. The potential dro appearing across the resistor l5 is impressed as a bias between the control electrode 24 and the cathode 25 through a resistor 21. The device 25 is provided with an anode 28 to which operating potential is supplied from the potential source 20 through a resistor 29. The connection of the discharge device 25 in this manner provides a phase inverter stage, the purpose of which is to impress across the output resistor 29 deflecting potentials of equal magnitude but of reversed phase to those appearing across the output resistor 2|.

The amplified deflecting potentials appearing across the resistors 2t and 29 in series are supplied through respective coupling condensers 3!], 3i to the deflecting electrodes 32, 33 provided in a cathode ray tube 34-. The cathode ray tube has a cathode 35 which is connected to ground and to the negative terminal of a source of relatively high potential 35. The positive terminal of the source 35 is connected through a resistor 3'! and 'a resistor 33 to the respective deflecting electrodes 32 and 33. The amplified deflecting potentials supplied through the coupling condensers 3%, 3| produce between the deflecting electrodes 32, 33 a periodically varying difference of potential which causes the electron stream of the oathode ray tube periodically to sweep across the fluorescent screen 39 provided in the end of the tube 34.

It will be understood that the cathode ray tube 34 is customarily provided with a second pair of deflecting electrodes, not shown, physically positioned at right angles to the deflecting electrodes 32, 33 and that a deflecting system similar to that shown is in practice connected to the second pair of deflecting electrodes. These deflecting electrodes and their deflecting system are omitted from the drawing for purposes of simplicity. It will further be understood, as is well known in the art, that the electron stream of the cathode ray tube 3 is modulated through a control circuit, not shown, by potentials impressed upon a control electrode 46] provided in the oathode ray tube to produce under the action of the deflecting electrodes 32, 33 and the second pair of deflecting electrodes, not shown, recurrent, superimposed, visual images on the fluorescent screen 39.

The source of potential 36 is here shown for purposes of simplicity as a battery. In practice, this potential is almost universally obtained by suitably rectifying and filtering an alternating current potential derived from a commercial power system. Since the potential of the source 35 is of the order of several thousand volts, it is relatively diflicult and somewhat expensive to remove all of the alternating current ripple and leave only a pure direct current potential. The use of such filters has been necessary heretofore since any ripples or pulsations which remain in this unidirectional potential are quite detrimental to the operation of the cathode ray tube 35 in that the alternating current component or ripple produces objectionable distortion of the reproduced image. This is the result of a flow of alternating current through the series circuits comprised, on the one hand, by the resistor 3'5, the condenser 33 and the resistor 2| in parallel with the anode to cathode path of the device 14 and the resistor l5, and on the other hand, by the resistor 38, the condenser 3 I and the resistor 29 in parallel with the anode to cathode space of the device 25 and the resistor l5. This ripple component of alternating current produces a corresponding variation of potential between the electrodes 32, 33 of the device 34 thus to give rise to the detrimental eflect on the visual image produced on the fluorescent screen 39 of the cathode ray tube.

The objectionable effect produced by ripple or pulsations occurring in the unidirectional potential 36 is avoided in a deflecting control system embodying my invention by proportioning the values of the several circuit constants in a manner now to be described.

If a ripple component is present in the potential supply 36 due to imperfect filtering of the rectified alternating current, there will be impressed between the deflecting electrode 32 and the cathode 35 an alternating current potential which has the value:

E R E32 R/+R37 where Eo=the ripple voltage occurring in the potential 36;

This same alternating current voltage is supplied through the coupling condenser 30 and appears as a ripple voltage across the resistor 2!.

A portion of the voltage which appears across the resistor 21 is inverted by the device 25 and appears across the resistor 23, and through the coupling condenser 23!, between the deflecting electrode 33 and the cathode 35 as a negative voltage of the same magnitude as E32. This is true because the purpose of the phaseinverter is to invert but not amplify the voltage which appears across the resistor 2|. I

The voltage appearing between the deflecting electrode 33 and the cathode 35 is thus made up of the sum of the ripple potential of the source 36 supplied through the resistor 38 and the ripple potential supplied through the coupling condenser 3i from the phase inverter stage. 'Expressed algebraically, this voltage is seen to have a value:

E0R E R 31 ss (2) where R"=the parallel resistance of resistor 29 and the plate resistance of the device 25; Rzs the resistance of resistor 33.

where En=the potential difierence between the deflecting electrodes 32 and 33.

The objectionable effect produced on the image pattern by the ripple voltage occurring in the potential source 36 may be avoided by giving the resistor 38 a value approximately one-half that of the resistor 31. Thus if R R R38:

'. the potential diiference betweenthe deflecting electrodes 3. and

In practicelR isin thejorderioi 50,Q'0 WhileRsq is in the orderpfidmegohmii Equation 6 is satisfied tol,within'a very..;fe cent for the condition'that nf 'ripple' v; appears between the deflecting electrodes" if v practice R3 ismade equalito oneehaliof'R a:

It will thusbe seen" thatby"givingtheresistorv 38 a particular value lessv than the value of the resistor 31, the ripple voltage occurring in the source 36 does not produce aipotential difference between the deflecting electrodes 32 and" 33L There is, therefore, no need to employ in a sweep system embodying my invention the relatively expensive filter heretofore necessarily employed to remove all ripple and the like pulsations from the potential of a source 36., Whether such ripple be of small or large magnitude, there is provided a deflecting system which may be' used with a source of unidirectional potential having'a relatively cheap and inefficient filtering 'sys',tem. This effects a marked saving inthe cost of the deflecting system for the cathode r y tube. f c

"While I have shown a particular, inloodirnfeI'll; of my invention, it will, of course; be understood; that I do not wish to "be'limite'd' thereto "since many modifications'maybe'made in" the'circ elements and their arrangement, and I therefore" contemplate by the appended claim std cover any such modifications as fall within" the; I" spirit and scope of my invention. c

What I claim as new and desire to secure by; Letters Patent of the United States is: i v 1. In combination, a cathode ray tube having a cathode and a pair of deflecting electrodes, means to supply operating potential between said cathode and eachiof said electrodes through respective impedances, means to supply signal potential across one of said impedances, and means to produce signal potentials across the other of said impedances in response to the potential on said one impedance, said last named means operating to produce signal potentials on said other impedance opposite in phase to that on said first impedance and to produce inequality between current variations in said impedances produced by irregularities of said operating potential, the values of said impedances being proportioned to equalize the potentials produced across said impedances by said unequal currents.

2. In combination, a cathode ray tube having a cathode and a pair of deflecting electrodes, means to supply operating potential between said cathode and each of said electrodes through respective impedances, means to supply signal potential across one of said impedances, and means to produce signal potentials across the other of said impedances in response to the potential on said one impedance, said last named means operating to produce signal potentials on said other impedance opposite in phase to that on said first impedance and to produce inequality between current variations in said impedances produced by irregularities of said operating potential, the value of said other impedance being substantially half that of said one impedance to equalize the potentials produced aoross' said impedances. by said unequalqcurs; re ts. 4 l 7 3.11m. combinationaai athode ray tub h ving. al -cathode: and; a pair of d flectin lectr des, means uto; upply x-operatina p t nt a b tween. said ca ho e and .eaohotxsa d electro esv through. respect v :.e anoe mean to supply control. po ent ls o equal ma ni de and opposing. phase acr ss respec v impedances. arran ed; in

-, a alle with sa d-re ista ces, said last named m ansson rati s'uto p odu e ineq al ty. between; cur ent iations in said resis ances p oduced t sofisai l opera in po en he. id resis ance bein proporti edqto e l ev-the noten lal p odu d acro s said restanoes by aidtune ualienrr n s v,

I l-co b nation; 1 2:; .cathode ray tube hayin -v h de and aPair-o .de et ns leetrod mean to sup l s rat nsoten a between aid cat o ea id. ea oi sa d electrodes th ou h respective esi an eaa pair o impe ances,, of substantially the same .ohmic value, ranged para le e o w th one s resi tances me nst.o,-. supp1y ig al p n i s a ross one oisa d impedances, means to produce signal potenti ls across the other of said impedances in response to the potential. on s aid one impedan e, ,1 1; lastlnan led means operating to produce signal potentials on .said other impedance oppositein phase to that on said first impedance and to produce undesirable inequality between current variations in said resistancesproduced by irregularities, of said operating potential, the values of v said resistances being proportioned to equaliz e the potentials produced across ,saidresistances by said unequal currents.

5. In combination, a cathode'ray tube havin at a d a p ir of de ect le tro es.

m ans o, su ply o ng potentia t een said cathode andeach of, said electrodes throughrespective' impedances, means to supply signal. potential across one of said impedances,;and means to produce. signal. potentials across the other of said impedances in response to the potential on said one impedance, said last named meansincluding means ,to Y produce signal poten-a tialson said other impedance opposite in phase to that on said first impedance and-t9 produce upon the occurrence of irregularities of said operating potential current in said other impedance which adds to the current produced through said other impedance by said irregularities of operating potential, the magnitude of said added currents through said other impedance being larger than the magnitude of the current produced through said one impedance by said irregularities of operating potential, the values of said impedances being proportioned to equalize the potentials produced across said impedances by said unequal currents.

6. In combination, a cathode ray discharge device having a cathode and a pair of deflecting electrodes, a pair of unequal resistances connected between said electrodes, a source of operating potential connected between said cathode and a point between said resistances, a pair of equal resistances connected between said electrodes, a pair of amplifiers each having a cathode, grid and anode, a source of operating potential therefor connected between said cathode and a point between said equal resistances, the outer terminals of said respective resistances being connected to the respective anodes of said amplifiers, means to supply cathode ray deflecting voltage through one of said amplifiers to one of said equal resistances and from said one equal resistance both to the higher valued of said unequal resistances'and through the other amplifier to the other of said equal resistances and thence to the lower-valued of said unequal resistances, whereby undesired variations of said first source are impressed upon said lower valued resistance both by reason of its direct circuit connection therewith and by reason of said lastmentioned amplifier, said lower valued resistance being so proportioned that the undesired voltage thereon equals the undesired voltage on the higher valued of said unequal resistances.

7. In combination, a cathode ray tube having apcathode and a pair of deflecting electrodes, means to supply operating potential having undesirable variations therein between said cathode and each of said electrodes through respective impedances, said impedances having unequal values,'an amplifier, means to supply deflecting potential through said amplifier to the higher valued of said impedances, means to supply signal potential from the output of said amplifier to the lower valued of said impedances in opposite phase to the signal potential on said higher valued impedance, the values of said impedances having a ratio to equalize the unde sired variations in voltage produced therein by said undesired variations in said operating potential.

8. In combination, a cathode ray tube having a cathode and a pair of deflecting electrodes, a source of operating potential subject to undesired variations having one side connected to said cathode and its other side connected through respective unequal impedances to said deflecting electrodes thereby producing undesired voltage variations on said impedances, means to supply deflecting voltage to one of said imped-i ances, and means to supply deflecting voltage of opposite phase from said means to the other impedance, said last means operating to supply said undesired variations from said one impedance to the other, the ratio of the values of said impedances being the inverse of the ratio of the undesired currents produ ced therein by said source and said last means whereby said undesired variations in voltages on. said impedances are equalized.

9;In' combination,v a cathode ray discharge apparatus having a. pair of deflecting electrodes and a cathode, a pair of impedances connected between said electrodes, a source of operating potential subject to undesired variations connected between said cathode and a point between said impedances, respective means effectively in shunt to each of said impedances to supply deflecting potential thereto, said means each being conductive to currents from said source having undesired variations therein and one of said means operating to supply variations corre sponding tothe undesired variations of said source from "the output of the other means to the impedance supplied by said one means whereby said last impedance carries undesired current variations from said source and from Said one means whereas the other impedance carries current only from said source, the product of the impedance of each of said impedances and the undesired current flowing therein being equal, whereby the undesired potentials on said impedances are equalized.

10. In combination, a cathode ray discharge apparatus having a pair of deflecting electrodes and a cathode, a pair of impedances connected between said electrodes, a source of operating potential subject to undesired variations connected between said cathode and a point between said impedances, respective means effectively in shunt to each of said impedances to supply deflecting potential thereto, said means each having sufliciently low impedance to undesired potential variations in said source that undesired amounts of such potential variations occur on said first impedances because of the low impedance of said means, and one of said means operating in addition to supply said undesired potential variations from the output of the other means to the impedance supplied by said one means, the impedances of said two means and the value of said two first-mentioned impedances being related to produce equal undesired potential variations on said first twoimpedances.

ROBERT B. DOME. 

